Curable inks comprising polymer-coated magnetic nanoparticles

ABSTRACT

There is provided novel curable ink compositions comprising polymer-coated magnetic metal nanoparticles. In particular, there is provided ultraviolet (UV) curable gel inks comprising at least the coated magnetic metal nanoparticles, one curable monomer, a radiation activated initiator that initiates polymerization of curable components of the ink, a gellant. The inks may also include optional colorants and one or more optional additives. These curable gel UV ink compositions can be used for ink jet printing in a variety of applications.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly owned and co-pending, U.S. patentapplication Ser. No. ______ (not yet assigned) entitled “Curable InksComprising Inorganic Oxide-Coated Magnetic Nanoparticles” to Iftime etal. (Attorney Docket No. 20101215-391169); U.S. patent application Ser.No. ______ (not yet assigned) entitled “Curable Inks Comprising CoatedMagnetic Nanoparticles” to Iftime et al. (Attorney Docket No.20101217-391168); U.S. patent application Ser. No. ______ (not yetassigned) entitled “Solvent-Based Inks Comprising Coated MagneticNanoparticles” to Iftime et al. (Attorney Docket No. 20101344-392137);U.S. patent application Ser. No. ______ (not yet assigned) entitled“Magnetic Curable Inks” to Iftime et al. (Attorney Docket No.20101090-US-NP); U.S. patent application Ser. No. ______ (not yetassigned) entitled “Phase Change Magnetic Ink Comprising Carbon CoatedMagnetic Nanoparticles And Process For Preparing Same,” to Iftime et al.(Attorney Docket No. 20100852-US-NP); U.S. patent application Ser. No.______ (not yet assigned) entitled “Solvent Based Magnetic InkComprising Carbon Coated. Magnetic Nanoparticles And Process ForPreparing Same” to Iftime et al. (Attorney Docket No. 20100896-US-NP);U.S. patent application Ser. No. ______ (not yet assigned) entitled“Phase Change Magnetic Ink Comprising Coated Magnetic Nanoparticles AndProcess For Preparing Same” to Iftime et al. (Attorney Docket No.20101180-US-NP); U.S. patent application Ser. No. ______ (not yetassigned) entitled “Phase Change Magnetic Ink Comprising Inorganic OxideCoated Magnetic Nanoparticles And Process For Preparing Same” to Iftimeet al. (Attorney Docket No. 20101182-US-NP); U.S. patent applicationSer. No. ______ (not yet assigned) entitled “Curable Inks ComprisingSurfactant-Coated Magnetic Nanoparticles” to Iftime et al. (AttorneyDocket No. 20101218-392253); U.S. patent application Ser. No. ______(not yet assigned) entitled “Solvent-Based Inks Comprising CoatedMagnetic Nanoparticles” to Iftime et al. (Attorney Docket No.20101347-391170); U.S. patent application Ser. No. ______ (not yetassigned) entitled “Phase Change Magnetic Ink Comprising SurfactantCoated Magnetic Nanoparticles and Process for Preparing the Same” toIftime et al. (Attorney Docket No. 20101179-US-NP); and U.S. patentapplication Ser. No. ______(not yet assigned) entitled “Phase ChangeMagnetic Ink Comprising Polymer Coated Magnetic Nanoparticles andProcess for Preparing the Same” to Iftime et al. (Attorney Docket No.20101181-US-NP), all filed electronically on the same day as the presentapplication, the entire disclosures of which are incorporated herein byreference in its entirety.

BACKGROUND

Non-digital inks and printing elements suitable for Magnetic InkCharacter Recognition (MICR) printing are generally known. The two mostcommonly known technologies are ribbon-based thermal printing systemsand offset technology. For example, U.S. Pat. No. 4,463,034 disclosesheat sensitive magnetic transfer element for printing MICR, comprising aheat resistant foundation and a heat sensitive imaging layer. Theimaging layer is made of ferromagnetic substance dispersed in a wax andis transferred on a receiving paper in the form of magnetic image by athermal printer which uses a ribbon. U.S. Pat. No. 5,866,637 disclosesformulations and ribbons which employ wax, binder resin and organicmolecule based magnets which are to be employed for use with a thermalprinter which employs a ribbon. MICR ink suitable for offset printingusing a numbering box are typically thick, highly concentrated pastesconsisting for example in about over 60% magnetic metal oxides dispersedin a base containing soy-based varnishes. Such inks are, for example,commercially available at Heath Custom Press (Auburn, Wash.). Digitalwater-based ink-jet inks composition for MICR applications using a metaloxide based ferromagnetic particles of a particle size of less than 500microns are disclosed in U.S. Pat. No. 6,767,396. Water-based inks arecommercially available from Diversified Nano Corporation (San Diego,Calif.).

The present embodiments are directed to curable inks. Curable inksgenerally comprise at least one curable monomer, a colorant, and aradiation activated initiator that initiates polymerization of curablecomponents of the ink. In particular, the curable ink is a ultraviolet(UV) curable liquid or gel ink. In particular, the curable ink is anultraviolet (UV) curable ink. These UV curable liquid or gel inkcompositions can be used for ink jet printing in a variety ofapplications. In addition to providing desirable ink qualities, thepresent embodiments are directed to magnetic inks for use in specificapplications. The curable UV ink of the present embodiments comprisesmagnetic nanoparticles that are coated with polymeric materials toprevent the exposure of the nanoparticles to oxygen.

UV curable gel inks are known. They are for example disclosed in, forexample, U.S. Pat. Nos. 7,153,349, 7,259,275, 7,270,408, 7,271,284,7,276,614, 7,279,506, 7,279,587, 7,293,868, 7,317,122, 7,323,498,7,384,463, 7,449,515, 7,459,014, 7,531,582, 7,538,145, 7,541,406,7,553,011, 7,556,844, 7,559,639, 7,563,489, 7,578,587, 7,625,956,7,632,546, 7,674,842, 7,681,966, 7,683,102, 7,690,782, 7,691,920,7,699,922, 7,714,040, 7,754,779, 7,812,064, and 7,820,731, thedisclosures of each of which are totally incorporated herein byreference. UV curable gel inks can exhibit desirable characteristicssuch as improved hardness and scratch-resistance and improved adhesionto various substrates. Curable gel inks can also exhibit advantages inthat dot spread of the ink can be controlled, the ink does not bleedexcessively into the substrate, including porous substrates.

The present embodiments are directed to UV curable magnetic inks whichcomprise polymer coated metal nanoparticles. These magnetic inks arerequired for specific applications such as Magnetic Ink CharacterRecognition (MICR) for automated check processing and security printingfor document authentication. One of the inherent properties of uncoatedmagnetic metal nanoparticles which precludes their use in thefabrication of commercial inks is their pyrophoric nature; uncoated(bare) magnetic nanoparticles of a certain size, typically in the orderof a few tens of nanometers or less, ignite spontaneously when exposedto oxygen in the ambient environment. As such, uncoated magnetic metalnanoparticles are a serious fire hazard. As such, large scale productionof the UV curable inks comprising such particles is difficult becauseair and water need to be completely removed when handling the particles.In addition, the ink preparation process is particularly challengingwith magnetic pigments because inorganic magnetic particles areincompatible with organic base components.

Thus, while the disclosed curable ink formulation provides someadvantages over the prior formulations, there is still a need to achievea formulation that not only provides the desirable properties of acurable ink and a curable liquid or gel UV ink in particular, but it isalso magnetic. Furthermore there is a need to achieve a magnetic curableink formulation that is easily produced and derived from components thatdo not require special handling conditions.

SUMMARY

According to embodiments illustrated herein, there is provided novelcurable ink compositions comprising polymer coated magnetic metalnanoparticles. A particular embodiment provides gel UV curable inkcompositions.

In particular, the present embodiments provided an ink comprising: acurable ink carrier comprising a monomer, a photoinitiator, an optionalcurable oligomer, and one or more optional additives; coated magneticnanoparticles, wherein the coated magnetic nanoparticles are comprisedof a magnetic metal core and a protective coating disposed on themagnetic metal core, wherein the protective coating comprises apolymeric material; and an optional colorant.

In further embodiments, there is provided an ink comprising: a curableink carrier comprising a monomer, a photoinitiator, an optional curableoligomer, and one or more optional additives; coated magneticnanoparticles, wherein the coated magnetic nanoparticles are comprisedof a magnetic metal core and a protective coating disposed on themagnetic metal core, wherein the protective coating comprises apolymeric material; a gellant; and an optional colorant.

In yet other embodiments, there is provided an ink comprising: a curableink carrier comprising a monomer, a photoinitiator, an optional curableoligomer, and one or more optional additives; coated magneticnanoparticles, wherein the coated magnetic nanoparticles are comprisedof a magnetic metal core and a protective coating disposed on themagnetic metal core, wherein the protective coating comprises apolymeric material; and an optional colorant, wherein the ink is usedfor Magnetic Ink Character Recognition applications.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present embodiments, reference may behad to the accompanying figures.

FIG. 1 illustrates a cross-section of a coated magnetic nanoparticleaccording to the present embodiments;

FIG. 2 illustrates a cross-section of a coated magnetic nanoparticleaccording to an alternative embodiment to FIG. 1; and

FIG. 3 illustrates a cross-section of a coated magnetic nanoparticleaccording to an alternative embodiment to FIG. 1 or FIG. 2.

DETAILED DESCRIPTION

In the following description, it is understood that other embodimentsmay be utilized and structural and operational changes may be madewithout departure from the scope of the present embodiments disclosedherein.

Curable ink technology broadens printing capability and customer baseacross many markets, and the diversity of printing applications will befacilitated by effective integration of printhead technology, printprocess and ink materials. As discussed above, while current ink optionsare successful for printing on various substrates, there is a need for amethod to produce magnetic curable inks comprising magnetic metalnanoparticles which reduces the safety risks associated with thenanoparticles.

The present embodiments are directed generally to ultraviolet (UV)curable magnetic inks and in a preferred embodiment to UV curable gelmagnetic inks. In particular, the present embodiments provide curableinks that are made with polymer coated magnetic metal nanoparticlesdispersed in a UV curable ink base. One of the inherent properties ofuncoated magnetic metal nanoparticles which precludes their use in thefabrication of commercial inks is their pyrophoric nature; uncoated(bare) magnetic nanoparticles ignite spontaneously when exposed tooxygen in the ambient environment. For example, bare iron, cobalt andalloys nanoparticles are a serious fire hazard. Thus, the presentembodiments provide a safe method for preparation of stable magnetic UVcurable inks suitable for applications that require the use of magneticinks. The present embodiments provide polymer coated magnetic metalnanoparticles which are protected from exposure to water and air. Thesenanoparticles have a coating of polymeric materials, such as forexample, poly(methyl methacrylate) (PMMA), polystyrene, polyesters andthe like, which acts as a barrier to water or air.

The present embodiments provide several advantages. For example, thecoated particles are easier to disperse in the ink base when comparedwith bare magnetic metal nanoparticles, and thus provides stabledispersions. The ink of the present embodiments is also easy to scale upbecause it eliminates oxidation processes and consequently the firehazard associated with uncoated magnetic metal nanoparticles. Thus, thepolymer-coated magnetic nanoparticles particles of the presentembodiments, when dispersed in an UV curable ink base with optionaladditives such as dispersants, provide a stable UV curable ink usefulfor different applications.

Magnetic inks are required for two main applications: (1) Magnetic InkCharacter Recognition (MICR) for automated check processing and (2)security printing for document authentication. The resulting curable inkcan be used for these applications.

The resulting curable ink can also be applied with piezo type inkjetprint heads suitable for both low and high temperature operationCurrently only water-based MICR inkjet ink are commercially available.Water based inks require special care of the printhead to preventevaporation of the ink or deposition of salts within the channelrendering the jetting ineffective. Furthermore high quality printingwith aqueous inks generally requires specially treated image substrates.In addition, there is generally a concern with respect to possibleincompatibility when operating both UV curable inks and water-based inkswithin the same printer. Issues like water evaporation due to theproximity to the organic curable heated ink tanks, rust, high humiditysensitivity of the UV ink are key problems which may preventimplementation of the water-based MICR solution. Thus, the presentembodiments further avoid these issues.

The present embodiments provide a UV curable ink made from coated metalmagnetic nanoparticles dispersed in a UV curable ink base. The ink basemay include one or more resins, one or more colorant, and/or one or moreadditives, such as, a gellant, dispersant and/or a dispersant/synergistcombination. In embodiments, the dispersant and/or synergist may not beneeded if the polymer coating material provide sufficient dispersibilityand stability of the nanoparticles in the ink base. Thus, selection ofthe dispersant and/or synergist depends on the type of protectivecoating.

The inks are suitable for use in various applications, including MICRapplications. In addition, the printed inks may be used for decorationpurposes, even if the resulting inks do not sufficiently exhibitcoercivity and remanence suitable for use in MICR applications. They mayalso be used for security printing applications. The coated magneticnanoparticles 5 are made of a core magnetic nanoparticle 15 coated onthe surface with a coating material 10 as shown in FIGS. 1-3. The coatedmagnetic nanoparticles can be produced to have different shapes such asoval (FIG. 1), cubed (FIG. 2), and spherical (FIG. 3). The shapes arenot limited to those depicted in the figures. Suitable polymer coatingmaterials may include a variety of materials, including for example,amorphous or crystalline, polymers and oligomers with a low molecularweight (for example, a M_(w) of from about 500 Daltons (Da) to about5000 Da and an M_(n) of about 100 Da to 5000 Da), polymers with a highmolecular weight (for example, a M_(w) of from about 5000 Da to about1,000,000 Da and M_(n) from about 1000 Da to about 1,000,000 Da),homopolymers, copolymers made of one or more types of monomers, and thelike and mixtures thereof.

The magnetic ink is made by dispersing the polymer-coated nanoparticlesin a UV curable ink base. The coating present on the surface of thenanoparticles provides air and moisture stability such that thenanoparticles are safer to handle.

Coating Materials for Magnetic Metal Nanoparticles

Various polymeric materials may be used for the nanoparticle coatingmaterials, and are suitable for producing protective coating layers forthe magnetic metal cores in nanoparticles. Suitable examples includePoly(methyl methacrylate) (PMMA), polystyrene, polyesters, and the like.Other suitable polymer materials include, without limitation,thermoplastic resins, homopolymers of styrene or substituted styrenessuch as polystyrene, polychloroethylene, and polyvinyltoluene; styrenecopolymers such as styrene-p-chlorostyrene copolymer, styrene-propylenecopolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalenecopolymer, styrene-methylacrylate copolymer, styrene-ethylacrylatecopolymer, styrene-butylacrylate copolymer, styrene-octylacrylatecopolymer, styrene-methylmethacrylate copolymer,styrene-ethylmethacrylate copolymer, styrene-butylmethacrylatecopolymer, styrene-methyl α-chloromethacrylate copolymer,styrene-acrylonitrile copolymer, styrene-vinylmethyl ether copolymer,styrene-vinylethyl ether copolymer, styrene-vinylmethyl ketonecopolymer, styrene-butadiene copolymer, styrene-isoprene copolymer,styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer,and styrene-maleic acid ester copolymer; polymethylmethacrylate;polybutylmethacrylate; polyvinylchloride; polyvinylacetate;polyethylene; polypropylene; polyester; polyvinylbutyral; polyacrylicresin; rosin; modified rosin; terpene resin; phenolic resin; aliphaticor aliphatic hydrocarbon resin; aromatic petroleum resin; chlorinatedparaffin; paraffin wax, and the like. Polymers can be homopolymers orcopolymers, linear or branched, random and block copolymers.

In further embodiments, oxygen barrier polymeric materials areparticularly suitable coating materials as they effectively block thenanoparticles from exposure to oxygen. Examples of oxygen barrierpolymeric materials include polyvinylidene chloride (PVDC), EthyleneVinyl Alcohol (EVOH), High Density Polyethylene (HDPE), NYLON 6 and thelike. Suitable oxygen barrier materials are also available from DowChemicals (SARAN series resins (e.g., SARAN 168 and SARAN 519)).

Copolymers are also suitable polymeric coating materials. For example, acopolymer made of PVDC and methyl acrylate monomers may be used forcoating. This copolymer is also available from Dow Chemicals (e.g.,SARAN XU 32019). Other examples include 10 L Blend, SARAN XU 32019.39Blend and SARAN XU 32019.40 Blend. Additionally, some of the oxygenbarrier polymers, particularly copolymers of PVDC with otherco-monomers, are soluble in various solvents at various temperatures asshown in Table 1.

TABLE 1 Temperature at which Polymer Material Solvent polymer dissolves(° C.) PVDC homopolymer N-methylpyrrolidine 42 PVDC homopolymertetramethylene 28 sufloxide PVDC homopolymer N-acetylpiperidine 34 PVDCcopolymers tetrahydrofuran <60 PVDC copolymers 1,4-dioxane 50-100 PVDCcopolymers cyclohexanone 50-100

The polymer coating on magnetic nanoparticles provides stability againstair and moisture but also increases compatibility of the magneticparticles with the ink base due to the fact that both the polymercoating and the ink base are organic materials. Thus, this compatibilityresults in good dispersibility of the magnetic nanoparticles as comparedto bare magnetic metal nanoparticles. As a result, there may besituations when, depending on the actual ink base components and thetype of polymer, a synergist or dispersant may not be required at all orthe amount needed is significantly decreased, thus saving extracomponents and costs.

Coatings and methods for coating particles with polymers layers aredescribed in, for example, Caruso, F., Advanced Materials, 13: 11-22(2001). Polymer coated nanoparticles can be obtained via synthetic andnon synthetic routes: polymerization of the particle surface; adsorptiononto the particles; surface modifications via polymerization processes;self-assembled polymer layers; inorganic and composite coatingsincluding precipitation and surface reactions and controlled depositionof preformed inorganic colloids; and use of biomacromolecular layer inspecific applications. A number of techniques for the preparation ofmagnetic nano- and micronized particles are also described in Journal ofSeparation Science, 30: 1751-1772 (2007).

Polystyrene-coated cobalt nanoparticles are described in U.S.Publication No. 2010/0015472 to Bradshaw, which is hereby incorporatedby reference. The disclosed process consists of thermal decomposition ofdicobalt octacarbonyl in dichlorobenzene as a solvent in the presence ofa polystyrene polymer terminated with a phosphine oxide group and anamine terminated polystyrene, at 160° C. under argon. The processprovided magnetic cobalt nanoparticles having a polymer coatingincluding a polystyrene shell. Additionally, other polymer shells can beplaced on the surface of the coated cobalt nanoparticles by exchange ofthe original polystyrene shell with other polymers. The referencefurther describes replacement of the polystyrene shell on coatednanoparticles by polymethylmethacrylate shell, through exchange reactionwith polymethylmethacrylate (PMMA) in toluene. These polymer coatedmagnetic nanoparticle materials are also suitable for fabrication ofmagnetic inks. U.S. Publication No. 2007/0249747 to Tsuji et al.discloses fabrication of polymer-coated metal nanoparticles frommagnetic FePt nanoparticles of a particle size of about 4 nm by stirringFePt nanoparticle dispersion in the presence of a —SH terminatedpolymer. Suitable polymers include PMMA.

The surface of magnetic nanoparticles can be modified: by grafting; atomtransfer radical polymerization (ATRP) and reversibleaddition-fragmentation chain transfer (RAFT) polymerization techniques(the latter using a chain transfer agent but no metal catalyst); solventevaporation method; layer by layer process; phase separation method;sol-gel transition; precipitation technique; heterogeneouspolymerization in the presence of magnetic particles;suspension/emulsion polymerization; microemulsion polymerization; anddispersion polymerization.

In addition to the known methods described above, a number of specifictechniques are of interest, such as for example, use of sonochemistryfor chemical grafting of anti-oxidant molecules with additionalhydrophobic polymer coating directly onto TiO₂ particle surfaces (Chem.Commun., 4815-4817 (2007)); use of pulse-plasma techniques (J. ofMacromolecular Science, Part B: Physics, 45: 899-909 (2006)); use ofsupercritical fluids and anti-solvent process for coating/encapsulationof microparticles with a polymer (J. of Supercritical Fluids, 28: 85-890(2004)); and use of electrohydrodynamic atomization for the productionof narrow-size-distribution polymer-pigment-nanoparticle composites.

Encapsulation/coating and surface modifications of nanoparticles, andparticularly magnetic nanoparticles with polymers, also provide usefulmethods that can be used to fabricate the ink of the presentembodiments. For example, polymer-coated iron nanoparticles may beformed by thermal decomposition of iron pentacarbonyl in a solvent inthe presence of a modified polymer structure with a terminal anchoringgroup, tetraethylenepentaamine (TEPA) (Burke et al., Chemical Materials,14: 4752-61 (2002)). After filtration and solvent removal, thecore-shell iron nanoparticles contain a shell made out of the polymericmaterial, for example, polyisobutylene (PIB), polystyrene (PS), andpolyethylene (PE). Polystyrene coated nanoparticles may be obtained bythermal decomposition of iron carbonyl gas in the presence of styrenemonomer by using plasma polymerization techniques (Srikanth et al.,Applied Physics Letters, 79: 3503-5 (2001)). The plasma generated heatinitiates fast decomposition of the iron carbonyl while at the same timethe styrene breaks down forming free radicals which initiate thepolymerization process on the surface of the generated ironnanoparticles.

The coating is disposed on the surface of the magnetic metalnanoparticles and may have a layer thickness of from about 0.2 nm toabout 100 nm, or from about 0.5 nm to about 50 nm, or from about 1 nm toabout 20 nm.

Although not limited to the above methods, all of the above methods maybe used to provide suitable polymer-coated magnetic nanoparticles neededfor fabrication of a magnetic UV curable ink according to the presentembodiments.

Magnetic Material

In embodiments, two types of magnetic metal based inks can be obtainedby the process herein, depending on the particle size and shape:ferromagnetic ink and superparamagnetic ink.

In embodiments, the metal nanoparticles herein can be ferromagnetic.Ferromagnetic inks become magnetized by a magnet and maintain somefraction of the saturation magnetization once the magnet is removed. Themain application of this ink is for Magnetic Ink Character Recognition(MICR) used for checks processing.

In embodiments, the metal nanoparticles herein can be superparamagneticinks. Superparamagnetic inks are also magnetized in the presence of amagnetic field but they lose their magnetization in the absence of amagnetic field. The main application of superparamagnetic inks is forsecurity printing, although not limited. In this case, an inkcontaining, for example, magnetic particles as described herein andcarbon black appears as a normal black ink but the magnetic propertiescan be detected by using a magnetic sensor or a magnetic imaging device.Alternatively, a metal detecting device may be used for authenticatingthe magnetic metal property of secure prints prepared with this ink. Aprocess for superparamagnetic image character recognition (i.e. usingsuperparamagnetic inks) for magnetic sensing is described in U.S. Pat.No. 5,667,924, which is hereby incorporated by reference herein in itsentirety.

As described above, the metal nanoparticles herein can be ferromagneticor superparamagnetic. Superparamagnetic nanoparticles have a remanentmagnetization of zero after being magnetized by a magnet. Ferromagneticnanoparticles have a remanent magnetization of greater than zero afterbeing magnetized by a magnet; that is, ferromagnetic nanoparticlesmaintain a fraction of the magnetization induced by the magnet. Thesuperparamagnetic or ferromagnetic property of a nanoparticle isgenerally a function of several factors including size, shape, materialselection, and temperature. For a given material, at a giventemperature, the coercivity (i.e. ferromagnetic behaviour) is maximizedat a critical particle size corresponding to the transition frommultidomain to single domain structure. This critical size is referredto as the critical magnetic domain size (Dc, spherical). In the singledomain range there is a sharp decrease of the coercivity and remanentmagnetization when decreasing the particle size, due to thermalrelaxation. Further decrease of the particle size results in completeloss of induced magnetization because the thermal effect become dominantand are sufficiently strong to demagnetize previously magneticallysaturated nanoparticles. Superparamagnetic nanoparticles have zeroremanence and coercivity. Particles of a size of about and above the Dcare ferromagnetic. For example, at room temperature, the Dc for iron isabout 15 nanometers for fcc cobalt is about 7 nanometers and for Nickelthe value is about 55 nm. Further, iron nanoparticles having a particlesize of 3, 8, and 13 nanometers are superparamagnetic while ironnanoparticles having a particle size of 18 to 40 nanometers areferromagnetic. For alloys, the Dc value may change depending on thematerials. For additional discussion of such details, see U.S. PatentPublication No. 20090321676 to Breton et al.; Burke, et al., Chemistryof Materials, pp. 4752-4761 (2002); B. D. Cullity and C. D. Graham,Introduction to Magnetic Materials, IEEE Press (Wiley), 2^(nd) Ed.,Chapter 11, Fine Particles and Thin Films, pp. 359-364 (2009); Lu et al.Angew. Chem. Int. Ed. 46:1222-444 (2007), Magnetic Nanoparticles:Synthesis, Protection, Functionalization and Application, which are allhereby incorporated by reference herein in their entirety.

In embodiments, the nanoparticle may be a magnetic metallicnanoparticle, that includes, for example, Co and Fe (cubic), amongothers. Others include Mn, Ni and/or alloys made of all of theforegoing. Additionally, the magnetic nanoparticles may be bimetallic ortrimetallic, or a mixture thereof. Examples of suitable bimetallicmagnetic nanoparticles include, without limitation, CoPt, fcc phaseFePt, fct phase FePt, FeCo, MnAI, MnBi, mixtures thereof, and the like.Examples of trimetallic nanoparticles can include, without limitationtri-mixtures of the above magnetic nanoparticles, or core/shellstructures that form trimetallic nanoparticles such as co-covered fctphase FePt.

The magnetic nanoparticles may be prepared by any method known in theart, including ball-milling attrition of larger particles (a commonmethod used in nano-sized pigment production), followed by annealing.The annealing is generally necessary because ball milling producesamorphous nanoparticles, which need to be subsequently crystallized intothe required single crystal form. The nanoparticles can also be madedirectly by RF plasma. Appropriate large-scale RF plasma reactors areavailable from Tekna Plasma Systems (Sherbrooke, Québec).

The average particle size of the magnetic nanoparticles may be, forexample, about 3 nm to about 300 nm in size in all dimensions. They canbe of any shape including spheres, cubes and hexagons. In oneembodiment, the nanoparticles are about 5 nm to about 500 nm in size,such as from about 10 nm to about 300 nm, or from 20 nm to about 250 nm,although the amount can be outside of these ranges. Herein, “average”particle size is typically represented as d₅₀, or defined as the medianparticle size value at the 50^(th) percentile of the particle sizedistribution, wherein 50% of the particles in the distribution aregreater than the d₅₀ particle size value, and the other 50% of theparticles in the distribution are less than the d₅₀ value. Averageparticle size can be measured by methods that use light scatteringtechnology to infer particle size, such as Dynamic Light Scattering. Theparticle diameter refers to the length of the pigment particle asderived from images of the particles generated by Transmission ElectronMicroscopy (TEM) or from Dynamic Light Scattering measurements.

The magnetic nanoparticles may be in any shape. Exemplary shapes of themagnetic nanoparticles can include, for example, without limitation,needle-shape, granular, globular, platelet-shaped, acicular, columnar,octahedral, dodecahedral, tubular, cubical, hexagonal, oval, spherical,densdritic, prismatic, amorphous shapes, and the like. An amorphousshape is defined in the context of the present embodiments as anill-defined shape having recognizable shape. For example an amorphousshape has no clear edges or angles. The ratio of the major to minor sizeaxis of the single nanocrystal (D major/D minor) can be less than about10:1, such as from about less than about 3:2, or less than about 2:1. Ina particular embodiment, the magnetic metal core has a needle-like shapewith an aspect ratio of from about 3:2 to about 10:1.

The loading requirements of the magnetic nanoparticles in the ink may befrom about 0.5 weight percent to about 30 weight percent, such as fromabout 5 weight percent to about 10 weight percent, or from about 6weight percent to about 8 weight percent, although the amount can beoutside of these ranges.

The magnetic nanoparticle can have a remanence of about 20 emu/g toabout 100 emu/g, such as from about 30 emu/g to about 80 emu/g, or about50 emu/g to about 70 emu/g, although the amount can be outside of theseranges.

The coercivity of the magnetic nanoparticle can be, for example, about200 Oersteds to about 50,000 Oersteds, such as from about 1,000 Oerstedsto about 40,000 Oersteds, or from about 10,000 Oersteds to about 20,000Oersteds, although the amount can be outside of these ranges.

The magnetic saturation moment may be, for example, about 20 emu/g toabout 150 emu/g, such as from about 30 emu/g to about 120 emu/g, or fromabout 40 emu/g to about 80 emu/g, although the amount can be outside ofthese ranges.

Carrier Material

The ink composition also includes a carrier material, or a mixture oftwo or more carrier materials.

In the case of a radiation (such as ultraviolet light) curable inkcomposition, the ink composition comprises a curable carrier material, aphotoinitiator, an optional colorant, and additional additives. Thecurable carrier material is typically a curable monomer, curableoligomer, and the like. The curable carrier may, in embodiments, includeone or more of these materials, including mixtures thereof. The curablematerials are typically liquid at 25° C. The curable ink composition canfurther include other curable materials, such as a curable wax or thelike, in addition to the colorant and other additives described above.The term “curable” refers, for example, to the component or combinationbeing polymerizable, that is, a material that may be cured viapolymerization, including, for example, free radical routes, and/or inwhich polymerization is photoinitiated though use of a radiationsensitive photoinitiator. Thus, for example, the term “radiationcurable” refers is intended to cover all forms of curing upon exposureto a radiation source, including light and heat sources and including inthe presence or absence of initiators. Example radiation curing routesinclude, but are not limited to, curing using ultraviolet (UV) light,for example having, a wavelength of 200-400 nm or more rarely visiblelight, such as in the presence of photoinitiators and/or sensitizers,curing using e-beam radiation, such as in the absence ofphotoinitiators, curing using thermal curing in the presence or absenceof high temperature thermal initiators (and which are generally largelyinactive at the jetting temperature), and appropriate combinationsthereof.

Suitable radiation-(such as UV-) curable monomers and oligomers include,but are not limited to, acrylated esters, acrylated polyesters,acrylated ethers, acrylated polyethers, acrylated epoxies, urethaneacrylates, and pentaerythritol tetraacrylate. Specific examples ofsuitable acrylated oligomers include, but are not limited to, acrylatedpolyester oligomers, such as CN2262 (Sartomer Co.), EB 812 (CytecSurface Specialties), EB 810 (Cytec Surface Specialties), CN2200(Sartomer Co.), CN2300 (Sartomer Co.), and the like, acrylated urethaneoligomers, such as EB270 (Cytec Surface Specialties), EB 5129 (CytecSurface Specialties), CN2920 (Sartomer Co.), CN3211 (Sartomer Co.), andthe like, and acrylated epoxy oligomers, such as EB 600 (Cytec SurfaceSpecialties), EB 3411 (Cytec Surface Specialties), CN2204 (SartomerCo.), CN110 (Sartomer Co.), and the like; and pentaerythritoltetraacrylate oligomers, such as SR399LV (Sartomer Co.) and the like.Specific examples of suitable acrylated monomers include, but are notlimited to) polyacrylates, such as trimethylol propane triacrylate,pentaerythritol tetraacrylate, pentaerythritol triacrylate,dipentaerythritol pentaacrylate, glycerol propoxy triacrylate,tris(2-hydroxyethyl)isocyanurate triacrylate, pentaacrylate ester, andthe like, epoxy acrylates, urethane acrylates, amine acrylates, acrylicacrylates, and the like. Mixtures of two or more materials can also beemployed as the reactive monomer. Suitable reactive monomers arecommercially available from, for example, Sartomer Co., Inc., BASFCorporation, Rahn AG., and the like. In embodiments, the at least oneradiation curable oligomer and/or monomer can be cationically curable,radically curable, or the like.

The curable monomer or oligomer in embodiments is included in the ink inan amount of, for example, about 20 to about 90 weight percent of theink, such as about 30 to about 85 weight percent, or about 40 to about80 weight percent, although the amount can be outside of these ranges.In embodiments, mixtures of curable monomer optionally with oligomer areselected to have a viscosity at 25° C. of about 1 to about 50 cP, suchas about 1 to about 40 cP or about 10 to about 30 cP, although theamount can be outside of these ranges. In one embodiment, the mixture ofcurable monomer and oligomer has a viscosity at 25° C. of about 20 cP.Also, in some embodiments, it is desired that the curable monomer oroligomer is not a skin irritant, so that uncured ink compositions arenot irritable to users.

Initiator

The ink compositions further comprise an initiator. Examples of freeradical initiators include benzyl ketones, monomeric hydroxyl ketones,polymeric hydroxyl ketones, α-amino ketones, acyl phosphine oxides,metallocenes, benzophenone, benzophenone derivatives, and the like.Specific examples include 1-hydroxy-cyclohexylphenylketone,benzophenone,2-benzyl-2-(dimethylamino)-1-(4-(4-morphorlinyl)phenyl)-1-butanone,2-methyl-1-(4-methylthio)phenyl-2-(4-morphorlinyl)-1-propanone,diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, benzyl-dimethylketal,isopropylthioxanthone (DAROCUR ITX, available from BASFBASF),2,4,6-trimethylbenzoyldiphenylphosphine oxide (available as BASF LUCIRINTPO), 2,4,6-trimethylbenzoylethoxyphenylphosphine oxide (available asBASF LUCIRIN TPO-L), bis(2,4,6-trimethylbenzoyl)-phenyl-phosphine oxide(available as BASF IRGACURE 819) and other acyl phosphines,2-methyl-1-(4-methylthio)phenyl-2-(4-morphorlinyl)-1-propanone(available as BASF IRGACURE 907) and1-(4-(2-hydroxyethoxy)phenyl)-2-hydroxy-2-methylpropan-1-one (availableas BASF IRGACURE 2959), 2-benzyl 2-dimethylamino1-(4-morpholinophenyl)butanone-1 (available as BASFBASF IRGACURE 369),2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)-benzyl)-phenyl)-2-methylpropan-1-one(available as BASF IRGACURE 127),2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-ylphenyl)-butanone(available as BASF IRGACURE 379), titanocenes, isopropylthioxanthone,1-hydroxy-cyclohexylphenylketone, 2,4,6-trimethylbenzophenone,4-methylbenzophenone, 2,4,6-trimethylbenzoylphenylphosphinic acid ethylester, oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone),2-hydroxy-2-methyl-1-phenyl-1-propanone, benzyl-dimethylketal,isopropyl-9H-thioxanthen-9-one, alpha amino ketone (IRGACURE 379), andthe like, as well as mixtures thereof.

Optionally, the curable inks can also contain an amine synergist, whichare co-initiators which can donate a hydrogen atom to a photoinitiatorand thereby form a radical species that initiates polymerization, andcan also consume dissolved oxygen, which inhibits free-radicalpolymerization, thereby increasing the speed of polymerization. Examplesof suitable amine synergists include (but are not limited to)ethyl-4-dimethylaminobenzoate, 2-ethylhexyl-4-dimethylaminobenzoate, andthe like, as well as mixtures thereof.

Initiators for inks disclosed herein can absorb radiation at any desiredor effective wavelength, in one embodiment at least about 200nanometers, and in one embodiment no more than about 560 nanometers, andin another embodiment no more than about 420 nanometers, although thewavelength can be outside of these ranges.

The initiator can be present in the ink in any desired or effectiveamount, in one embodiment at least about 0.5 percent by weight of thecarrier, and in another embodiment at least about 1 percent by weight ofthe carrier, and in one embodiment no more than about 15 percent byweight of the carrier, and in another embodiment no more than about 10percent by weight of the carrier, although the amount can be outside ofthese ranges.

Colorants

The MICR ink as prepared is either black or dark brown. In furtherembodiments, the MICR ink according to the present disclosure may befurther produced as a colored ink by adding a colorant during inkproduction. Alternatively, a MICR ink lacking a colorant may be printedon a substrate during a first pass, followed by a second pass, wherein acolored ink that is lacking MICR particles is printed directly over thecolored ink, so as to render the colored ink MICR-readable. This can beachieved through any means known in the art. For example, each ink canbe stored in a separate reservoir. The printing system delivers each inkseparately to the substrate, and the two inks interact. The inks may bedelivered to the substrate simultaneously or consecutively. Any desiredor effective colorant can be employed in the ink compositions, includingpigment, dye, mixtures of pigment and dye, mixtures of pigments,mixtures of dyes, and the like. The coated magnetic nanoparticles mayalso, in embodiments, impart some or all of the colorant properties tothe ink composition.

Suitable colorants for use in the MICR ink according to the presentdisclosure include, without limitation, carbon black, lamp black, ironblack, ultramarine, Nigrosine dye, Aniline Blue, Du Pont Oil Red,Quinoline Yellow, Methylene Blue Chloride, Phthalocyanine Blue,Phthalocyanine Green, Rhodamine 6C Lake, Chrome Yellow, quinacridone,Benzidine Yellow, Malachite Green, Hansa Yellow C, Malachite Greenhexylate, oil black, azo oil black, Rose Bengale, monoazo pigments,disazo pigments, trisazo pigments, tertiary-ammonium salts, metallicsalts of salicylic acid and salicylic acid derivatives, Fast Yellow G3,Hansa Brilliant Yellow 5GX, Disazo Yellow AAA, Naphthol Red HFG, LakeRed C, Benzimidazolone Carmine HF3CS, Dioxazine Violet, BenzimidazoloneBrown HFR. Aniline Black, titanium oxide, Tartrazine Lake, Rhodamine 6GLake, Methyl Violet Lake, Basic 6G Lake, Brilliant Green lakes, HansaYellow, Naphtol Yellow, Watching Red, Rhodamine B, Methylene Blue,Victoria Blue, Ultramarine Blue, and the like.

The amount of colorant can vary over a wide range, for instance, fromabout 0.1 to about 50 weight percent, or from about 3 to about 20 weightpercent, and combinations of colorants may be used.

Additional Additives

The ink of the present embodiments may further contain one or moreadditives for their known purposes. For example, suitable additivesinclude, a wax, a dispersant, a cross-linking agent, a stabilizer, aviscosity modifier, an antioxidant and a gellant.

Wax

The cured images are very robust and one or more waxes may be added tothe MICR inkjet ink. The wax can be present in an amount of, forexample, from about 0.1 to about 10 weight percent, or from about 1 toabout 6 weight percent based on the total weight of the ink composition,although the amount can be outside of these ranges. Examples of suitablewaxes include, but are not limited to, polyolefin waxes, such as lowmolecular weight polyethylene, polypropylene, copolymers thereof andmixtures thereof. Other examples include a polyethylene wax, apolypropylene wax, a fluorocarbon-based wax (Teflon), or Fischer-Tropschwax, although other waxes can also be used.

In one specific embodiment the wax can be a curable wax. These waxes canbe synthesized by the reaction of a wax containing a transformablefunctional group, such as carboxylic acid or hydroxyl with a reagentcontaining curable or polymerizable groups. Suitable examples of waxescontaining hydroxyl groups include hydroxyl-terminated polyethylenewaxes and Guerbet alcohols which are characterized as 2,2-dialkyl-1ethanols. Suitable waxes containing carboxylic acid transformable groupinclude carboxylic acid terminated polyethylenes and Guerbet acids whichare characterized as 2,2-dialkyl ethanoic acids. The curable groupspresent can include, but are not limited to, acrylate, methacrylate,alkene, alkyne, vinyl, and allylic ether.

The wax can be present in the ink in any desired or effective amount, inone embodiment at least about 1 percent, in another embodiment at leastabout 2 percent, and in yet another embodiment at least about 3 percent,and in one embodiment no more than about 40 percent, in anotherembodiment no more than about 30 percent, and in yet another embodimentno more than about 20 percent, by weight of the ink carrier, althoughthe amounts can be outside of these ranges.

Gellant

The ink composition can also optionally contain a gellant. The gellantcan function to increase dramatically the viscosity of the radiationcurable phase change ink within a desired temperature range. Inparticular, the gellant can form a semi-solid gel in the ink carrier attemperatures below the specific temperature at which the ink is jetted.The semi-solid gel phase in a specific embodiment is a physical gel thatexists as a dynamic equilibrium comprising one or more solid gellantmolecules and a liquid solvent. The semi-solid gel phase is believed tobe a dynamic networked assembly of molecular components held together bynon-covalent bonding interactions such as hydrogen bonding, Van derWaals interactions, aromatic non-bonding interactions, ionic orcoordination bonding, London dispersion forces, or the like, which uponstimulation by physical forces such as temperature or mechanicalagitation or chemical forces such as pH or ionic strength, can undergo areversible transition from liquid to semi-solid state at the macroscopiclevel. The inks exhibit a thermally reversible transition between thesemi-solid gel state and the liquid state when the temperature is variedabove or below the gel phase transition of the ink. This reversiblecycle of transitioning between semi-solid gel phase and liquid phase canbe repeated many times in the ink formulation. Mixtures of one or moregellants can be used to effect the phase-change transition.

Specific examples of gellants include curable amide gellants asdisclosed in U.S. Pat. No. 7,714,040, trans-1,2-cyclohexanebis(urea-urethane) compounds as disclosed in, for example, U.S. Pat. No.7,153,349, curable epoxy-polyamides as disclosed in, for example, U.S.Pat. No. 7,563,489, the disclosure of all of which are totallyincorporated herein by reference.

Examples of suitable gellant materials include, but are not limited to,curable amide gellants as disclosed in U.S. Pat. No. 7,714,040, thedisclosure of which is totally incorporated herein by reference, such asthose of the formula

wherein:

R₁ and R₁′ each, independently of the other, is: (i) an alkyl group,(ii) an arylalkyl group, or (iii) an alkylaryl group; R₂ and R₂′ each,independently of the other, are: (i) alkylene groups, (ii) arylenegroups, (iii) arylalkylene groups, or (iv) alkylarylene groups; R₃ is:(i) an alkylene group, (ii) an arylene group, (iii) an arylalkylenegroup, or (iv) an alkylarylene group; and n is an integer representingthe number of repeat amide units, being in one embodiment at least 1,and in one embodiment no more than about 20, in another embodiment nomore than about 15, and in yet another embodiment no more than about 10,although the value of n can be outside of these ranges.

Other examples of suitable gellants are compounds are those described inU.S. Pat. Nos. 7,276,614 and 7,279,587, the entire disclosures of whichare incorporated herein by reference.

As described in U.S. Pat. No. 7,279,587, the amide gellant may be acompound of the formula

wherein:

R₁ is:

(i) an alkylene group (wherein an alkylene group is a divalent aliphaticgroup or alkyl group, including linear and branched, saturated andunsaturated, cyclic and acyclic, and substituted and unsubstitutedalkylene groups, and wherein heteroatoms, such as oxygen, nitrogen,sulfur, silicon, phosphorus, boron, and the like either may or may notbe present in the alkylene group) having from about 1 carbon atom toabout 12 carbon atoms, such as from about 1 carbon atom to about 8carbon atoms or from about 1 carbon atom to about 5 carbon atoms,

(ii) an arylene group (wherein an arylene group is a divalent aromaticgroup or aryl group, including substituted and unsubstituted arylenegroups, and wherein heteroatoms, such as oxygen, nitrogen, sulfur,silicon, phosphorus, boron, and the like either may or may not bepresent in the arylene group) having from about 1 carbon atom to about15 carbon atoms, such as from about 3 carbon atoms to about 10 carbonatoms or from about 5 carbon atoms to about 8 carbon atoms,

(iii) an arylalkylene group (wherein an arylalkylene group is a divalentarylalkyl group, including substituted and unsubstituted arylalkylenegroups, wherein the alkyl portion of the arylalkylene group can belinear or branched, saturated or unsaturated, and cyclic or acyclic, andwherein heteroatoms, such as oxygen, nitrogen, sulfur, silicon,phosphorus, boron, and the like either may or may not be present ineither the aryl or the alkyl portion of the arylalkylene group) havingfrom about 6 carbon atoms to about 32 carbon atoms, such as from about 6carbon atoms to about 22 carbon atoms or from about 6 carbon atoms toabout 12 carbon atoms, or

(iv) an alkylarylene group (wherein an alkylarylene group is a divalentalkylaryl group, including substituted and unsubstituted alkylarylenegroups, wherein the alkyl portion of the alkylarylene group can belinear or branched, saturated or unsaturated, and cyclic or acyclic, andwherein heteroatoms, such as oxygen, nitrogen, sulfur, silicon,phosphorus, boron, and the like either may or may not be present ineither the aryl or the alkyl portion of the alkylarylene group) havingfrom about 5 carbon atoms to about 32 carbon atoms, such as from about 6carbon atoms to about 22 carbon atoms or from about 7 carbon atoms toabout 15 carbon atoms,

wherein the substituents on the substituted alkylene, arylene,arylalkylene, and alkylarylene groups can be halogen atoms, cyanogroups, pyridine groups, pyridinium groups, ether groups, aldehydegroups, ketone groups, ester groups, amide groups, carbonyl groups,thiocarbonyl groups, sulfide groups, nitro groups, nitroso groups, acylgroups, azo groups, urethane groups, urea groups, mixtures thereof, andthe like, wherein two or more substituents can be joined together toform a ring;

R₂ and R₂′ each, independently of the other, are:

(i) alkylene groups having from about 1 carbon atom to about 54 carbonatoms, such as from about 1 carbon atom to about 48 carbon atoms or fromabout 1 carbon atom to about 36 carbon atoms,

(ii) arylene groups having from about 5 carbon atoms to about 15 carbonatoms, such as from about 5 carbon atoms to about 13 carbon atoms orfrom about 5 carbon atoms to about 10 carbon atoms,

(iii) arylalkylene groups having from about 6 carbon atoms to about 32carbon atoms, such as from about 7 carbon atoms to about 33 carbon atomsor from about 8 carbon atoms to about 15 carbon atoms, or

(iv) alkylarylene groups having from about 6 carbon atoms to about 32carbon atoms, such as from about 6 carbon atoms to about 22 carbon atomsor from about 7 carbon atoms to about 15 carbon atoms,

wherein the substituents on the substituted alkylene, arylene,arylalkylene, and alkylarylene groups may be halogen atoms, cyanogroups, ether groups, aldehyde groups, ketone groups, ester groups,amide groups, carbonyl groups, thiocarbonyl groups, phosphine groups,phosphonium groups, phosphate groups, nitrile groups, mercapto groups,nitro groups, nitroso groups, acyl groups, acid anhydride groups, azidegroups, azo groups, cyanato groups, urethane groups, urea groups,mixtures thereof, and the like, and wherein two or more substituents maybe joined together to form a ring;

R₃ and R₃′ each, independently of the other, are either:

(a) photoinitiating groups, such as groups derived from1-(4-(2-hydroxyethoxy)phenyl)-2-hydroxy-2-methylpropan-1-one, of theformula

groups derived from 1-hydroxycyclohexylphenylketone, of the formula

groups derived from 2-hydroxy-2-methyl-1-phenylpropan-1-one, of theformula

groups derived from N,N-dimethylethanolamine orN,N-dimethylethylenediamine, of the formula

or the like, or:(b) a group which is:

(i) an alkyl group (including linear and branched, saturated andunsaturated, cyclic and acyclic, and substituted and unsubstituted alkylgroups, and wherein heteroatoms, such as oxygen, nitrogen, sulfur,silicon, phosphorus, boron, and the like either may or may not bepresent in the alkyl group) having from about 2 carbon atoms to about100 carbon atoms, such as from about 3 carbon atoms to about 60 carbonatoms or from about 4 carbon atoms to about 30 carbon atoms,

(ii) an aryl group (including substituted and unsubstituted aryl groups,and wherein heteroatoms, such as oxygen, nitrogen, sulfur, silicon,phosphorus, boron, and the like either may or may not be present in thearyl group) having from about 5 carbon atoms to about 100 carbon atoms,such as from about 5 carbon atoms to about 60 carbon atoms or from about6 carbon atoms to about 30 carbon atoms, such as phenyl or the like,

(iii) an arylalkyl group (including substituted and unsubstitutedarylalkyl groups, wherein the alkyl portion of the arylalkyl group canbe linear or branched, saturated or unsaturated, and cyclic or acyclic,and wherein heteroatoms, such as oxygen, nitrogen, sulfur, silicon,phosphorus, boron, and the like either may or may not be present ineither the aryl or the alkyl portion of the arylalkyl group) having fromabout 5 carbon atoms to about 100 carbon atoms, such as from about 5carbon atoms to about 60 carbon atoms or from about 6 carbon atoms toabout 30 carbon atoms, such as benzyl or the like, or

(iv) an alkylaryl group (including substituted and unsubstitutedalkylaryl groups, wherein the alkyl portion of the alkylaryl group canbe linear or branched, saturated or unsaturated, and cyclic or acyclic,and wherein heteroatoms, such as oxygen, nitrogen, sulfur, silicon,phosphorus, boron, and the like either may or may not be present ineither the aryl or the alkyl portion of the alkylaryl group) having fromabout 5 carbon atoms to about 100 carbon atoms, such as from about 5carbon atoms to about 60 carbon atoms or from about 6 carbon atoms toabout 30 carbon atoms, such as tolyl or the like,

wherein the substituents on the substituted alkyl, arylalkyl, andalkylaryl groups may be halogen atoms, ether groups, aldehyde groups,ketone groups, ester groups, amide groups, carbonyl groups, thiocarbonylgroups, sulfide groups, phosphine groups, phosphonium groups, phosphategroups, nitrile groups, mercapto groups, nitro groups, nitroso groups,acyl groups, acid anhydride groups, azide groups, azo groups, cyanatogroups, isocyanato groups, thiocyanato groups, isothiocyanato groups,carboxylate groups, carboxylic acid groups, urethane groups, ureagroups, mixtures thereof, and the like, and wherein two or moresubstituents may be joined together to form a ring; and X and X′ each,independently of the other, is an oxygen atom or a group of the formula—NR₄—, wherein R₄ is:

(i) a hydrogen atom;

(ii) an alkyl group, including linear and branched, saturated andunsaturated, cyclic and acyclic, and substituted and unsubstituted alkylgroups, and wherein heteroatoms either may or may not be present in thealkyl group, having from about 5 carbon atoms to about 100 carbon atoms,such as from about 5 carbon atoms to about 60 carbon atoms or from about6 carbon atoms to about 30 carbon atoms,

(iii) an aryl group, including substituted and unsubstituted arylgroups, and wherein heteroatoms either may or may not be present in thearyl group, having from about 5 carbon atoms to about 100 carbon atoms,such as from about 5 carbon atoms to about 60 carbon atoms or from about6 carbon atoms to about 30 carbon atoms,

(iv) an arylalkyl group, including substituted and unsubstitutedarylalkyl groups, wherein the alkyl portion of the arylalkyl group maybe linear or branched, saturated or unsaturated, and cyclic or acyclic,and wherein heteroatoms either may or may not be present in either thearyl or the alkyl portion of the arylalkyl group, having from about 5carbon atoms to about 100 carbon atoms, such as from about 5 carbonatoms to about 60 carbon atoms or from about 6 carbon atoms to about 30carbon atoms, or

(v) an alkylaryl group, including substituted and unsubstitutedalkylaryl groups, wherein the alkyl portion of the alkylaryl group canbe linear or branched, saturated or unsaturated, and cyclic or acyclic,and wherein heteroatoms either may or may not be present in either thearyl or the alkyl portion of the alkylaryl group, having from about 5carbon atoms to about 100 carbon atoms, such as from about 5 carbonatoms to about 60 carbon atoms or from about 6 carbon atoms to about 30carbon atoms,

wherein the substituents on the substituted alkyl, aryl, arylalkyl, andalkylaryl groups may be halogen atoms, ether groups, aldehyde groups,ketone groups, ester groups, amide groups, carbonyl groups, thiocarbonylgroups, sulfate groups, sulfonate groups, sulfonic acid groups, sulfidegroups, sulfoxide groups, phosphine groups, phosphonium groups,phosphate groups, nitrile groups, mercapto groups, nitro groups, nitrosogroups, sulfone groups, acyl groups, acid anhydride groups, azidegroups, azo groups, cyanato groups, isocyanato groups, thiocyanatogroups, isothiocyanato groups, carboxylate groups, carboxylic acidgroups, urethane groups, urea groups, mixtures thereof, and the like,and wherein two or more substituents may be joined together to form aring.

Also suitable as gellants are aromatic ester-terminated diamidecompounds of the formula

wherein R₁ and R₁′ can be the same or different and wherein R₁ and R₁′each, independently of the other, can be groups such as

R₂ and R₂′ include groups such as isomers of the formula —C₃₄H_(56+a)—which are branched alkylene groups which may include unsaturations andcyclic groups, wherein a is an integer of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11, or 12, and R₃ includes groups such as —CH₂CH₂—, as disclosed in,for example, U.S. application Ser. No. 12/765,148, filed Apr. 22, 2010,entitled “Amide Gellant Compounds with Aromatic End Groups,” with thenamed inventors Naveen Chopra, Michelle N. Chrétien, Barkev Keoshkerian,Jennifer L. Belelie, and Peter G. Odell, the disclosure of which istotally incorporated herein by reference.

Also suitable as gellants are trans-1,2-cyclohexane bis(urea-urethane)compounds as disclosed in, for example, U.S. Pat. No. 7,153,349, thedisclosure of which is totally incorporated herein by reference, such asthose of the formula

or mixtures thereof, wherein R₁ and R′₁ each, independently of theother, is (i) an alkylene group, (ii) an arylene group, (iii) anarylalkylene group, or (iv) an alkylarylene group, R₂ and R′₂ each,independently of the other, is (i) an alkyl group, (ii) an aryl group,(iii) an arylalkyl group, or (iv) an alkylaryl group, R₃ and R′₃ each,independently of the other, is a hydrogen atom or an alkyl group, R₄ andR′₄ each, independently of the other, is a hydrogen atom, a fluorineatom, an alkyl group, or a phenyl group, n is an integer of 0, 1 2, 3,or 4, and each R₅, independently of the others, is (i) an alkyl group,(ii) an aryl group, (iii) an arylalkyl group, (iv) an alkylaryl group,or (v) a substituent other than an alkyl, aryl, arylalkyl, or alkylarylgroup.

Antioxidant

The ink composition can also optionally contain an antioxidant. Theoptional antioxidants of the ink compositions protect the images fromoxidation and also protect the ink components from oxidation during theheating portion of the ink preparation process. Specific examples ofsuitable antioxidants include NAUGUARD® series of antioxidants such asNAUGUARD® 445, NAUGUARD® 524, NAUGUARD® 76, and NAUGUARD® 5112(commercially available from Chemtura Corporation, Philadelphia, Pa.),the IRGANOX® series of antioxidants such as IRGANOX® 10310 (commerciallyavailable from BASF), and the like. When present, the optionalantioxidant can be present in the ink in any desired or effectiveamount, such as in an amount of from at least about 0.01 to about 20percent by weight of the ink, such as about 0.1 to about 5 percent byweight of the ink, or from about 1 to about 3 percent by weight of theink, although the amount can be outside of these ranges.

Viscosity Modifier

The ink composition can also optionally contain a viscosity modifier. Inparticular embodiments, the viscosity controlling agent may be selectedfrom the group consisting of aliphatic ketones, such as stearone, andthe like, polymers such as polystyrene, polymethylmethacrylate, and thelike, and thickening agents such as those available from BYK Chemie.When present, the optional viscosity modifier can be present in the inkin any desired or effective amount, such as about 0.1 to about 99percent by weight of the ink, such as about 1 to about 30 percent byweight of the ink, or about 10 to about 15 percent by weight of the ink,although the amount can be outside of these ranges.

Dispersants

Dispersant may be optionally present in then ink formulation. The roleof the dispersant is to further ensure improved dispersion stability ofthe coated magnetic nanoparticles by stabilizing interactions with thecoating material. Suitable dispersants include but not limited to, oleicacid, trioctyl phosphine oxide (TOPO), hexyl phosphonic acid (HPA),polyvinylpyrrolidone (PVP), and combinations thereof. Additionalsuitable dispersants include beta hydroxy carboxylic acids and theiresters containing long linear, cyclic or branched aliphatic chains, suchas those having about 5 to about 60 carbons, such as pentyl, hexyl,cyclohexyl, heptyl, octyl, nonyl, decyl, undecyl, and the like; sorbitolesters with long chain aliphatic carboxylic acids such as lauric acid,oleic acid (SPAN® 85), palmitic acid (SPAN® 40), and stearic acid (SPAN®60); polymeric compounds such as polyvinylpyrrolidone,poly(1-vinylpyrrolidone)-graft-(1-hexadecene),poly(1-vinylpyrrolidone)-graft-(1-triacontene), poly(1vinylpyrrolidone-co-acrylic acid), and combinations thereof. Inembodiments, the dispersant is selected from the group consisting ofoleic acid, lauric acid, palmitic acid, stearic acid, trioctyl phosphineoxide, hexyl phosphonic acid, polymeric compounds likepolyvinylpyrrolidone, poly(1-vinylpyrrolidone)-graft-(1-hexadecene),poly(1-vinylpyrrolidone)-graft-(1-triacontene), poly(1vinylpyrrolidone-co-acrylic acid), pentyl, hexyl, cyclohexyl, heptyl,octyl, nonyl, decyl, or undecyl beta-hydroxy carboxylic acid, sorbitolesters with long chain carboxylic acid and combinations thereof.Suitable dispersants also include the SOLSPERSE series from LubrizolCorp (Wickliffe, Ohio), which comprise sulfonic groups; the EFKA seriesof dispersants including brand numbers 4340, 4585, 7476, 7496 from BASF;and Byk 2001 or Byk 2155 from Bykchemie.

A suitable amount of dispersant can be selected, such as in an amount ofabout 0.1 to about 10 weight percent, such as from about 0.2 to about 5weight percent of the ink weight, although the amount can be outside ofthese ranges. The choice of particular dispersants or combinationsthereof as well as the amounts of each to be used are within the purviewof those skilled in the art.

Preparation of Ink

The ink composition of the present disclosure can be prepared by anydesired or suitable method. For example, in the case of curable gel UVinks the ink ingredients can be mixed together, followed by heating,typically to a temperature of from about 50° C. to about 100° C.,although the temperature can be outside of this range, and stirringuntil a homogeneous ink composition is obtained, followed by cooling theink to ambient temperature (typically from about 20° C. to about 25°C.). In the case of liquid ink compositions, the ink ingredients cansimply be mixed together with stirring to provide a homogeneouscomposition, although heating can also be used if desired or necessaryto help form the composition. Other methods for making ink compositionsare known in the art and will be apparent based on the presentdisclosure.

Printing of the Ink

The magnetic metal particle ink may generally be printed on a suitablesubstrate such as, without limitation, paper, glass art paper, bondpaper, paperboard, Kraft paper, cardboard, semi-synthetic paper orplastic sheets, such as polyester or polyethylene sheets, and the like.These various substrates can be provided in their natural state; such asuncoated paper, or they can be provided in modified forms, such ascoated or treated papers or cardboard, printed papers or cardboard, andthe like.

Specific suitable papers include plain papers such as XEROX 4200 papers,XEROX Image Series papers, ruled notebook paper, bond paper, silicacoated papers such as Sharp Company silica coated paper, JuJo paper,HAMMERMILL LASERPRINT paper, and the like, glossy coated papers such asXEROX Digital Color Gloss, Sappi Warren Papers LUSTROGLOSS, specialtypapers such as Xerox DURAPAPER, and the like.

Further suitable materials may be used, including but not limited to,transparency materials, fabrics, textile products, plastics, polymericfilms, inorganic recording mediums such as metals and wood, and thelike, transparency materials, fabrics, textile products, plastics,polymeric films, inorganic substrates such as metals and wood, and thelike.

The ink of the present disclosure may be used in both MICR and non-MICRapplications.

The inks described herein are further illustrated in the followingexamples. All parts and percentages are by weight unless otherwiseindicated.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also,various presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art, and are also intended to beencompassed by the following claims.

While the description above refers to particular embodiments, it will beunderstood that many modifications may be made without departing fromthe spirit thereof. The accompanying claims are intended to cover suchmodifications as would fall within the true scope and spirit ofembodiments herein.

The presently disclosed embodiments are, therefore, to be considered inall respects as illustrative and not restrictive, the scope ofembodiments being indicated by the appended claims rather than theforegoing description. All changes that come within the meaning of andrange of equivalency of the claims are intended to be embraced therein.

EXAMPLES

The examples set forth herein below and are illustrative of differentcompositions and conditions that can be used in practicing the presentembodiments. All proportions are by weight unless otherwise indicated.It will be apparent, however, that the present embodiments can bepracticed with many types of compositions and can have many differentuses in accordance with the disclosure above and as pointed outhereinafter.

Example 1 Fabrication of a Magnetic Ink Concentrate with Polymer CoatedMagnetic Nanoparticles

1.a. Polymer Coated Nanoparticles

Polystyrene coated cobalt, nanoparticles are obtained by thermaldecomposition of dicobalt octacarbonyl in dichlorobenzene as a solventin the presence of a polystyrene polymer terminated with a phosphineoxide group, and an amine terminated polystyrene in a ratio of 4:1 (w/w)at 160 deg. C. under argon for 30 min. The reaction mixture isprecipitated into hexane and further washed to provide polystyrenecoated cobalt nanoparticles. The fabrication process is described inUS2010/0015472 A1 (Bradshaw).

1.b. Magnetic Ink Concentrate

To an attritor loaded with zirconia shots (1800 g) is added apropoxylated neopentyl diacrylate curable monomer (SR9003, 57.6 g,obtained from Sartomer Co. Inc., Exeter, Pa.) and 27.4 g of EFKA 4340 (adispersant consisting of an acrylic block copolymer in methoxypropanolavailable from BASF; the methoxypropanol was removed by distillationbefore use). The mixture is stirred at 200 r.p.m. and then to this areadded 15 g of polymer coated magnetic nanoparticles (US2010/0015472 A1(Bradshaw) over a 1 minute period. This mixture is then stirred for 20hours and then sieved to remove the zirconia shot to afford a 15%dispersion of polymer coated magnetic nanoparticles.

1.c. General Procedure for Fabrication of Curable Gel UV Magnetic Inks

An UV curable phase-change ink containing polymer coated magneticparticles is prepared as follows. To a 600 mL beaker equipped with amagnetic stir bar and enclosed within a jacketed heating mantle is addedthe monomer(s) and photoinitiators. The mixture is covered with foil andstirred with heating to 90° C. Next, amide gellant and wax are added andstirring is continued until the mixture is homogeneous. This clear inkbase is filtered under pressure through a heated 1 μm filter. Thefiltered ink base is transferred to another 600 mL beaker enclosedwithin a jacketed heating mantle heated to 90° C. and a homogenizer isimmersed. The 15% dispersion of polymer coated magnetic nanoparticlesdispersion concentrate is added to the ink base during homogenizationand the mixture is blended for 40 minutes. Then the ink is filteredagain under pressure through a heated 1 um filter to furnish the finalink.

Ink base compositions are described below for gel inks (PropheticExample 2) and ink with no gellant (Prophetic Example 3).

Example 2 Magnetic UV Ink Containing Gellant and Wax

An ink composition containing a gellant, which is the same as the onedisclosed in Ink Example A of U.S. Pat. No. 7,714,040, the disclosure ofwhich is totally incorporated herein by reference, and wax according tothe present embodiments is described in Table 2.

TABLE 2 Component Wt % Amide Gellant 7.5 UNILIN 350 Wax Acrylate 5SR399LV Monomer 5 IRGACURE 379 3 IRGACURE 819 1 IRGACURE 127 3.5IRGASTAB UV10 0.2 20 wt % Magnetic Particle 74.8 Dispersion/SR9003Monomer TOTAL 100

Example 3 Magnetic UV Ink Without Gellant and Wax

An ink composition without gellant and wax according to the presentembodiments is described in Table 3.

TABLE 3 Component Wt % SR9003 Monomer 12.5 SR399LV Monomer 5 IRGACURE379 3 IRGACURE 819 1 IRGACURE 127 3.5 IRGASTAB UV10 0.2 20 wt % MagneticParticle 74.8 Dispersion/SR9003 Monomer TOTAL 100

Magnetic Ink Curing

Drops of the ink from Prophetic Examples or 2 are deposited on paperwith a pipette. The drops were cured by passing the ink coated paperunder a 600 W Fusion UV Systems, Inc. Lighthammer lamp fitted with amercury D-bulb at a belt speed of 32 feet per minute. A thin skin isvisible on the surface of the droplets indicating that curing has takenplace.

SUMMARY

In summary, the present embodiments provide a magnetic UV curable inkcompositions made by using polymer-coated magnetic nanoparticlesdispersed in an UV curable ink base with optional colorants. The coatingmaterial may include a variety of polymeric materials and may befabricated in a number of ways, as described herein. The inks aresuitable for MICR and security applications. Moreover, the use ofstabilized magnetic nanoparticles allows for safe and scalable magneticUV curable ink fabrication by using processes generally suitable forpigmented inks as the protected particles are a reduced fire hazard whencompared with bare particles). In addition, UV curable ink bases bothwith and without phase change gellants are suitable for the variousapplications.

The claims, as originally presented and as they may be amended,encompass variations, alternatives, modifications, improvements,equivalents, and substantial equivalents of the embodiments andteachings disclosed herein, including those that are presentlyunforeseen or unappreciated, and that, for example, may arise fromapplicants/patentees and others. Unless specifically recited in a claim,steps or components of claims should not be implied or imported from thespecification or any other claims as to any particular order, number,position, size, shape, angle, color, or material.

All the patents and applications referred to herein are herebyspecifically, and totally incorporated herein by reference in theirentirety in the instant specification

1. A black or dark brown ink comprising: a curable ink carriercomprising a monomer, a photoinitiator, an optional curable oligomer,and one or more optional additives; coated magnetic nanoparticles,wherein the coated magnetic nanoparticles are comprised of a magneticmetal core and a protective coating disposed on the magnetic metal core,wherein the protective coating comprises a polymeric material, whereinthe coated magnetic nanoparticles is present in an amount of about 0.5weight percent to about 30 weight percent of the ink; and an optionalcolorant.
 2. The ink according to claim 1, wherein the magnetic metalcore is selected from the group consisting of Fe, Mn, Co, Ni, FePt,CoPt, MnAI, MnBi and mixtures thereof.
 3. The ink according to claim 1,wherein the polymeric materials are selected from the group consistingof amorphous homopolymers and copolymers, crystalline homopolymers andcopolymers, polymers and oligomers with a M_(w) of from about 500Daltons to about 5000 Daltons and an M_(n) from about 100 to 500,polymers and oligomers with a M_(w) of from about 5000 Daltons to about1,000,000 Daltons and an M_(n) from about 1000 to 1,000,000, andmixtures thereof.
 4. The ink according to claim 3, wherein the polymericmaterials are selected from the group consisting of poly(methylmethacrylate), polystyrene, polyesters, polyamides, polyvinylidenechloride, ethylene vinyl alcohol (EVOH), polyethylene, styrenecopolymers with p-chlorostyrene, propylene, vinyltoluene,vinylnaphthalene, methyl acrylate, ethyl acrylate, butyl acrylate, octylacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate,methyl α-chloromethacrylate, acrylonitrile copolymer, vinyl methylether, vinyl ethyl ether, vinyl methyl ketone, butadiene, isoprene,acrylonitrile-indene, maleic acid, and maleic acid ester; polybutylmethacrylate; polyvinyl chloride; polyvinyl acetate; polypropylene;polyvinyl butyral; polyacrylic resin; rosin; modified rosin; terpeneresin; phenolic resin; aliphatic or aliphatic hydrocarbon resin;aromatic petroleum resin; chlorinated paraffin; paraffin wax, andmixtures thereof.
 5. The ink according to claim 3, wherein the polymericmaterial is an oxygen barrier material.
 6. The ink according to claim 1,wherein the protective coating comprises a polymer terminated with afunctional group which is selected from the group consisting of amide,amine, carboxylic acid, phosphine oxide, carboxylic ester, alcohol,thiol, and mixtures thereof.
 7. The ink according to claim 1, whereinthe protective coating has a thickness of from about 0.2 nm to about 100nm.
 8. The ink according to claim 1, wherein the magnetic nanoparticleshave a remanence of about 20 emu/gram to about 100 emu/gram.
 9. The inkaccording to claim 1, wherein the magnetic nanoparticles have acoercivity of about 200 Oersteds to about 50,000 Oersteds.
 10. The inkaccording to claim 1, wherein the magnetic nanoparticles have a magneticsaturation moment of from about 20 emu/gram to about 150 emu/gram. 11.The ink according to claim 1, wherein a size of the nanoparticles in alldimensions is about 3 nm to about 300 nm.
 12. The ink according to claim1, wherein the magnetic metal core has a shape selected from the groupconsisting of needle-shaped, granular, globular, cube, hexagonal, oval,spherical and amorphous.
 13. The ink according to claim 1, wherein themagnetic metal core has a needle-like shape with an aspect ratio of fromabout 3:2 to about 10:1.
 14. The ink according to claim 1, wherein thecarrier is present in an amount of about 30 to about 99.5 weight percentand the colorant is present in an amount of about 0.1 to about 50 weightpercent of the ink.
 15. The ink according to claim 1 wherein the monomeris selected from the group consisting of acrylated esters, acrylatedpolyesters, acrylated ethers, acrylated polyethers, acrylated epoxies,urethane acrylates, pentaerythritol tetraacrylate, dipentaerythritolpentaacrylate, and mixtures thereof.
 16. The ink according to claim 1,wherein the initiator is selected from a group consisting of benzylketones, monomeric hydroxyl ketones, polymeric hydroxyl ketones, α-aminoketones, acyl phosphine oxides, metallocenes, benzophenone, benzophenonederivatives, and mixtures thereof.
 17. The ink according to claim 1,wherein the one or more additives are selected from the group consistingof a wax, a dispersant, a synergist, a stabilizer, a viscosity modifier,a clarifier, and mixtures thereof.
 18. A black or dark brown inkcomprising: a curable ink carrier comprising a monomer, aphotoinitiator, an optional curable oligomer, and one or more optionaladditives; coated magnetic nanoparticles, wherein the coated magneticnanoparticles are comprised of a magnetic metal core and a protectivecoating disposed on the magnetic metal core, wherein the protectivecoating comprises a polymeric material, wherein the coated magneticnanoparticles is present in an amount of about 0.5 weight percent toabout 30 weight percent of the ink; a gellant; and an optional colorant.19. The ink according to claim 18, wherein the gellant is selected froma group consisting of: (a) a polyamide with the general structure:

wherein n is an integer between 1 and 5; R₁ is (i) an alkylene group,(ii) an arylene group, (iii) an arylalkylene group (iv) an alkylarylenegroup; R₂ and R₂′ each, independently of the other, are (i) alkylenegroups (ii) arylene groups, (iii) arylalkylene groups (iv) alkylarylenegroups; and R₃ and R₃′ each, independently of the other, are either (A)photoinitiating groups, or (B) groups which are (i) alkyl groups, (ii)aryl groups (iii) arylalkyl groups (iv) alkylaryl groups, and X and X′each, independently of the other, is an oxygen atom or a group of theformula NR₄, wherein R₄ is (i) a hydrogen atom, (ii) an alkyl group,(iii) an aryl group, (iv) an arylalkyl group, or (v) an alkylaryl group;(b) a curable amide gellant; (c) an ester-terminated diamide compound;and (d) a trans-1,2-cyclohexane-bis(urea-urethane) compound.
 20. An inkcomprising: a curable ink carrier comprising a monomer, a photoinitiator, an optional curable oligomer, and one or more optionaladditives; coated magnetic nanoparticles, wherein the coated magneticnanoparticles are comprised of a magnetic metal core and a protectivecoating disposed on the magnetic metal core, wherein the protectivecoating comprises a polymeric material, and further wherein thepolymeric materials are selected from the group consisting of amorphoushomopolymers and copolymers, crystalline homopolymers and copolymers,polymers and oligomers with a Mw of from about 500 Daltons to about 5000Daltons and an Mn from about 100 to 500, polymers and oligomers with aMw of from about 5000 Daltons to about 1,000,000 Daltons and an Mn fromabout 1000 to 1,000,000, and mixtures thereof; and an optional colorant,wherein the ink is used for Magnetic Ink Character Recognition (MICR)applications.